Lightweight support mat for equipment and vehicles

ABSTRACT

A lightweight rig mat comprises a cellular soil stabilization material, with a plastic foam injected into the cells of the cellular material to provide required load-carrying capacity. The cellular material is preferably treated with a bonding agent to promote a structural bond between the plastic foam and the cellular material, thereby enhancing the overall shear strength, structural integrity, and flexural rigidity of the mat. The cell walls may also have textured surfaces to enhance the bond with the foam. The walls between the cells in the cellular material may have perforations to permit foam to flow between cells during the foam-injection process. The mat may be formed with connector pockets to facilitate interconnection of adjacent mats using suitable connection means, so as to prevent lateral separation between mats while allowing articulation between adjacent mats to accommodate irregular ground surfaces.

FIELD OF THE DISCLOSURE

The present disclosure relates in general to support mats used over soft or unstable ground surfaces for temporarily supporting vehicles and equipment at construction sites, oil well drilling sites, and other temporary installations.

BACKGROUND OF THE INVENTION

Temporary support mats are commonly used for supporting equipment and vehicle loads at drilling rig sites, construction sites, and in other applications, particularly in locations where soil conditions are soft or weak. Similar mats may also be used in permanent applications—for example, by being incorporated into roadway and embankment substructures to distribute loads over poor subsoils. Such support mats are commonly referred to as rig mats or road mats. For convenience, the term “rig mat” will be used in this patent document as a non-limiting term intended to encompass support mats for purposes as mentioned above and for similar or analogous purposes.

Rig mats need to have structural strength and durability to withstand loadings and impact forces that they can be subjected to from vehicular and stationary equipment at drilling rig sites and construction sites. Individual rig mats must be sized for transport to the rig site, such as by flatbed trailer (8′×14′×6″ is a common rig mat size). Rig mats are preferably provided with means for interconnecting individual mats after they have been positioned on site, to prevent both lateral and vertical separation between individual mats in response to applied loadings. It is also desirable for rig mats to be resistant to corrosion and other types of physical deterioration that can result from their exposure to a range of climatic conditions and in some cases to other environmental conditions (such as industrial chemicals).

There are various known types of rig mats, with perhaps the simplest and most widely-known type being the wooden rig mat. These are simple and comparatively economical to build, but they are prone to impact damage and environmental damage. They are also quite heavy (especially rig mats made from oak or other dense hardwoods), which makes them more expensive to transport because fewer mats can be transported in a given shipment due to truck and roadway loading restrictions.

Some of the drawbacks of wooden rig mats are addressed by other mat designs such as steel mats; wood/steel mats; solid HDPE (high-density polyethylene) mats; engineered hollow HDPE matting systems; rubber mats made from recycled tire materials; and fiberglass-coated foam mats. However, these types of mats also have drawbacks. Steel and wood/steel mats are still heavy, and they are more costly than wood mats. HDPE mats, rubber mats, and fiberglass-coated foam mats may be considerably lighter than wooden mats, but they can be considerably more costly.

For these reasons, there is a need for rig mats that are lighter than wooden mats and more resistant to climatic and environmental deterioration, while having sufficient strength and durability to withstand in-service loadings and impacts, yet economically competitive with wooden mats.

BRIEF SUMMARY

The present disclosure teaches a lightweight rig mat incorporating a cellular soil stabilization material, with a plastic foam injected or poured into the cells of the cellular material to provide required structural load-carrying capacity. The cellular material is preferably treated with a suitable bonding agent to promote a structural bond between the plastic foam and the cellular material, thereby enhancing the overall shear strength, structural integrity, and flexural rigidity of the mat. The cell walls may also have textured surfaces to enhance the bond with the foam. The walls between the cells in the cellular material preferably have perforations to permit foam to flow between cells during the foam-injection or filling process.

One non-limiting example of a cellular soil stabilization material suitable for purposes of the disclosed rig mat is EnviroGrid® made by Geo Products. L.L.C., of Houston, Tex. The EnviroGrid® material is made from multiple strips of polymeric material stacked or nested together with intermittent bonding zones whereat adjacent strips are structurally connected. The material may then be expanded to form a cellular structure.

The original intended purpose of the EnviroGrid® material and similar cellular products is soil stabilization, such as for erosion control and reinforcement of roadways and earthen embankments. For these uses, the cellular material is filled with gravel or other soil material and incorporated into the earthwork structure under construction (e.g., road base, embankment, etc.). The cellular structure of the material confines the gravel fill, thus preventing lateral displacement and enhancing the stability and strength of the earthwork structure. To the inventor's knowledge, the use of such cellular material for purposes of constructing rig mats has not been previously contemplated, and nor has it been previously contemplated to fill such cellular materials with a plastic foam for any purpose.

The foam used for rig mats in accordance with the present disclosure is not limited to any particular type. Examples of suitable foam include polyurethane foam such as Dow® STYROFOAM™ spray polyurethane foam (SPF), a two-component spray-applied foam insulation which has been used with effective results in experimental testing of prototype rig mats in accordance with the present disclosure. Other suitable foam materials include expanded polystyrene (for example, Styropor® manufactured by BASF), which has been used for many years in roadway and embankment construction, and Dow® Hi-Load 60 or Dow® Hi-Load 100. To enhance the overall structural strength of the rig mats, a reinforcing material such as Fibermesh® (available from Propex Concrete Systems Corp. of Chattanooga, Tenn.) may optionally be mixed into the foam prior to injection into the cellular material.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments in accordance with the present disclosure will now be described with reference to the accompanying Figures, in which numerical references denote like parts, and in which:

FIG. 1 is an isometric view of a first embodiment of a rig mat in accordance with the present disclosure.

FIG. 2 is an enlarged isometric detail of a section of the foam-filled cellular core of a rig mat as in FIG. 1.

FIG. 3 is a plan view illustrating one possible field layout of rig mats in accordance with the present disclosure.

FIG. 4 is a sectional detail illustrating one alternative means for interconnecting rig mats in accordance with the present disclosure.

DETAILED DESCRIPTION

FIG. 1 illustrates a rig mat 10 comprising a cellular material 20 defining a plurality of cells 22 enclosed by cell walls 23, with at least some and preferably all of cell walls 23 having perforations 21. Rig mat 10 will typically be rectilinear as illustrated, but rig mats 10 in accordance with the present disclosure could alternatively be provided in non-rectilinear configurations.

Although not shown in FIG. 1, cells 22 are filled with a structural foam 70 (as designated by filled cells 22F in FIG. 2). In the illustrated embodiment, a perimeter enclosure band 30 is provided around the sides of the cellular material 20, preferably prior to foam-filling operations so that the half-cells 24 formed between enclosure band 30 and side regions of the cellular material 20 can be filled with foam at the same time as inner cells 22. However, enclosure band 30 is optional, and embodiments not having an enclosure band 30 are intended to come within the scope of the present disclosure.

Although not necessarily required for all embodiments of rig mats in accordance with the present disclosure, in preferred embodiments a top skin 32 is applied over the upper surface of the foam-filled cellular material 20 as shown in FIGS. 1, 3, and 4. As best seen in FIG. 4, rig mat 10 preferably also has a bottom skin 34, which may be applied after the cellular material 20 is filled with foam or prior to that operation. Enclosure band 30, top skin 32, and bottom skin 34 may be made from any suitable material, such as but not limited to polyurethane (which may be applied by spraying over the foam-filled cellular material) or HDPE sheet material. Suitable bonding agents will preferably be used to promote and enhance bonding and structural continuity between enclosure band 30, top skin 32, and/or bottom skin 34, and cellular material 20 and/or the foam 70 in cells 22 and half-cells 24.

To facilitate interconnection between multiple rig mats 10 in service, rig mats 10 optionally may be fabricated with connector pockets 40 at selected locations around the perimeter of each rig mat 10. In the embodiments shown in FIGS. 1 and 3, each rig mat 10 has four connector pockets 40, one at each corner, with connector pockets 40 being provided in the form of pipe stubs (preferably but not necessarily cut from plastic piping). However, other embodiments may incorporate more or fewer connector pockets 40, and in different locations than shown herein. In embodiments using pipe stubs or similar items to form connector pockets 40, any suitable means can be provided if and as necessary for retaining the stubs in position during rig mat fabrication and for integrating them into the completed rig mat assembly.

As seen in FIG. 1, the incorporation of pipe stubs or similar pocket-forming items into rig mat 10 may result in the formation of interstitial spaces 26 between the pipe stubs and adjacent cell walls 23, and such interstitial spaces 26 will preferably be filled with foam 70 along with cells 22 and half-cells 24. At least a portion of each connector pocket 40 will preferably be kept free of foam fill to facilitate insertion of mat connectors as described later herein.

Referring now to FIGS. 3 and 4, adjacent rig mats 10 can be interconnected in the field by use of suitable anchors, shown by way of non-limiting illustration in FIG. 4 in the form of C-shaped connection bars 50 having end legs 52 within connector pockets 40 of adjacent rig mats 10. After installation of connection bars 50, the associated connector pockets 40 may optionally be filled with a suitable hard-setting or semi-rigid filler material 60 to restrain connection bars 50 from shifting and allowing relative lateral displacement between adjacent rig mats 10.

In accordance with another (and unillustrated) non-limiting example of how adjacent rig mats can be laterally interconnected, connection bars having a generally S-shaped configuration may be used, with the central leg of each connection bar being disposed between two adjacent mats, with one free-end leg disposed in an upward orientation within a connector pocket in a first mat, and with the other free-end leg disposed in a downward orientation within a connector pocket in a second mat.

Alternatively, connectors for joining adjacent rig mats may be sized and configured for a fairly close tolerance fit within the connector pockets, so as to prevent significant lateral displacement between adjacent mats without need for using a filler material in the connector pockets.

The optional use of mat connection means as described above will help to prevent significant lateral separation if any between adjacent mats while allowing articulation between adjacent mats to accommodate irregular ground surfaces.

Support mats constructed in accordance with the present disclosure can provide structural strength and durability sufficient to withstand loads and environmental exposures that can be expected in many practical applications, including on drilling rig sites, construction sites, and both temporary and permanent roadway structures, while being considerably lighter in weight than other types of mats. This translates to economic savings in terms of shipping costs, as more mats of this type (i.e., with a greater surface area) can be shipped on a given transport vehicle than other, heavier types of mats, without exceeding highway load limits. These savings can be particularly significant when mats need to be shipped to remote locations, which is commonly the case for rig sites and construction sites. Additional economies can be realized in terms of equipment and labor costs for loading and on-site handling of the mats, due to their comparatively light weight.

When used in temporary or permanent roadway construction, mats in accordance with the present disclosure provide both structural strength and insulation for protection against frost heave. As previously noted herein, it is known to use cellular materials such as EnviroGrid® to reinforce roadway and embankment structures. The usual procedure is to prepare the ground surface that is to receive the cellular material, then expand the accordion-like cellular material over the ground surface, pin the material to the ground using spikes or other suitable means, fill the cells of the cellular material with granular material using heavy equipment, and then add 6 to 10 inches of additional granular material over the filled cellular material. If frost heave is a potential concern, a layer of insulation boards (e.g., HDPE or expanded polystyrene) will be placed under the cellular material. Using mats as taught herein, however, the same practical benefits, in terms of both structural reinforcement and insulation value, can be achieved faster and with significantly reduced need for heavy equipment. The light, foam-filled cellular mats are simply laid over the prepared ground surface and then covered with a protective granular layer, with the required structural and insulating properties being incorporated into the mats.

It will be readily appreciated by those skilled in the art that various modifications of the present invention may be devised without departing from the scope and teaching of the present invention, including modifications which may use equivalent structures or materials hereafter conceived or developed. It is to be especially understood that the invention is not intended to be limited to any described or illustrated embodiment, and that the substitution of a variant of a claimed element or feature, without any substantial resultant change in the working of the invention, will not constitute a departure from the scope of the invention.

In this patent document, any form of the word “comprise” is to be understood in its non-limiting sense to mean that any item following such word is included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one such element is present, unless the context clearly requires that there be one and only one such element. Any use of any form of the terms “connect”, “bond”, or any other term describing an interaction between elements is not meant to limit the interaction to direct interaction between the subject elements, and may also include indirect interaction between the elements such as through secondary or intermediary structure.

Wherever used in this document, the terms “typical” and “typically” are to be interpreted in the sense of representative or common usage or practice, and are not to be understood as implying invariability or essentiality. 

What is claimed is:
 1. A rig mat comprising a cellular material defining a plurality of cells enclosed by cell walls, with said cells being filled with a structural foam to form a foam-filled cellular panel of substantially uniform thickness and having an upper surface, a lower surface, and a perimeter.
 2. A rig mat as in claim 1 wherein the at least some of the cell walls have perforations.
 3. A rig mat as in claim 1, further comprising an enclosure band around the perimeter of the foam-filled cellular panel.
 4. A rig mat as in claim 1, further comprising a top skin covering the upper surface of the foam-filled cellular panel and a bottom skin covering the lower surface of the foam-filled cellular panel.
 5. A rig mat as in claim 3, further comprising a top skin covering the upper surface of the foam-filled cellular panel and a bottom skin covering the lower surface of the foam-filled cellular panel.
 6. A rig mat as in claim 1, further comprising interconnection means, for interconnection with a laterally-adjacent rig mat.
 7. A rig mat as in claim 6, wherein the interconnection means comprises one or more connector pockets.
 8. A method for constructing a rig mat structure, said method comprising the steps of: (a) providing a plurality of rig mats in accordance with claim 7; (b) arranging the plurality of rig mats over a ground surface with each rig mat laterally adjacent to at least one other rig mat; (c) providing a plurality of connection bars, each having two end legs and configured such that one of the end leg can be disposed within a selected connector pocket in a first rig mat and the other end leg can be disposed within a selected connector pocket in an adjacent second rig mat; and (d) for each connection bar, disposing one of its end legs within a selected connector pocket in a first rig mat and disposing the other end leg within a selected connector pocket in an adjacent second rig mat.
 9. A method as in claim 8, further comprising the step of introducing a filler material into each connector pocket receiving an end leg of a connection bar.
 10. A method as in claim 8 wherein at least one connection bar has a generally C-shaped configuration.
 11. A method as in claim 8 wherein at least one connection bar has a generally S-shaped configuration. 